Cholera is a serious diarrheal disease caused by the pathogenic strains of Vibrio cholerae, which leads to severe dehydration and even death within 18 hours if left untreated. Indeed, the World Health Organization (WHO) has estimated that 3 to 5 million cases of cholera occur each year with approximately 100,000 to 130,000 of those cases ending in death.
Despite the severity of cholera, cholera is generally no longer a concern in developed countries. However, it is still a major threat in many developing countries, where a safe water supply and advanced sanitation systems are generally not available. In fact, large outbreaks of cholera sporadically occur every year, as recently seen in Papua New Guinea (2009-2010), Zimbabwe and other African countries (2008-2010), as well as, most recently, in Haiti (2010-present).
Due to recurring outbreaks, implementation of a mass vaccination program for cholera has now been proposed as part of global cholera prevention strategies. Dukoral (Crucell, Netherlands) is an internationally licensed, World Health Organization-prequalified oral cholera vaccine, which contains killed Vibrio cholerae bacteria and a recombinant cholera toxin B subunit polypeptide (rCTB; SEQ ID NO: 2) produced in genetically-modified bacterium. This vaccine has been shown to provide protection in greater than 80% of subjects to which it is administered, which is higher than killed V. cholerae alone. Nevertheless, production of sufficient doses of the vaccine for mass vaccination campaigns has proven to be challenging, particularly for the rCTB, whose production is significantly hindered by the limited scalability of fermentation-based production.